This thesis focuses on enhancing the predictive accuracy of the ShorelineS one-dimensional (1D) coastline model, which is used to simulate coastal evolution. The research primarily addresses the limitation of ShorelineS, which excludes cross-shore sediment redistribution, impacting its ability to predict coastal changes, as demonstrated in the case of the Bacton Sandscaping project.

The Bacton Sandscaping project was designed to counter coastal erosion threatening the Bacton Gas Terminal, a crucial part of the UK's energy infrastructure. Instead of traditional hard engineering solutions, a soft approach, inspired by the Dutch Sand Engine, was chosen. This method involves depositing a large volume of sand along the coast, which is gradually redistributed by natural forces to offer long-term protection. Despite the project’s success, challenges were identified in modeling the coastline's evolution, particularly with ShorelineS, which only considers longshore sediment transport. This thesis explores how incorporating cross-shore redistribution into ShorelineS can improve its predictive capability, especially for large-scale nourishment projects like Bacton.

The research begins by evaluating ShorelineS in its current form, comparing modeled and observed coastline changes. The model tends to underestimate erosion near the gas terminal and overestimate sediment distribution to nearby villages, leading to inaccuracies. To address this, a redistribution factor (R-factor) is introduced, which adjusts the model based on observed cross-shore changes. The R-factor is applied to the terminal section, improving predictions slightly, though overall performance remains limited due to the model's sediment conservation assumptions.

The study concludes that cross-shore redistribution significantly affects coastline evolution, as seen in the Bacton case. Although the R-factor improves predictions somewhat, the limitations of ShorelineS, such as its sediment retention assumptions and the CERC2 transport equation, suggest that further model refinements are necessary. Future research should explore alternative approaches to cross-shore redistribution, more frequent coastline updates, and sensitivity analyses to enhance the model's accuracy in predicting the evolution of mega nourishment projects.

Coastal regions, particularly beaches, are vital and dynamic areas for human activities. They serve various functions and are crucial barriers safeguarding coastal cities. However, the beach faces an increase in population and natural hazards caused by climate change are creating new challenges that coastal engineers are working to address.

This study introduces a new technique, SHORECAST (Satellite-derived Historical and future Orientation-based Relation for Estimating Coastline Adjustments and Sediment Transport), to enhance the Satellite-derived Shorelines (SDS). This technique is designed to estimate the shoreline dynamics in front of the shoreline and predict shoreline positions globally, offering a quick and accessible alternative to the existing models. The primary objective of this study is to employ shoreline position data obtained from SDS to estimate Longshore Sediment Transport (LST) and predict shoreline position quickly and effortlessly.

To achieve the study's objective, SHORECAST is developed and adapted into a multi-step framework using the annual dataset from the Shoreline Monitor of Luijendijk et al. (2018). The dataset assesses sandy and non-sandy beaches and their historical shoreline position at transects every 500 meters along the coast for the last 37 years. Only sandy shoreline evolutions are considered for the development of this new tool. First, a routine is developed to find coastal cells to which the research's aim could be applied. Secondly, multiple algorithms were deployed on the coastal cells to obtain the historical shoreline orientation and the LST. Combining these values leads to a correlation for predicting shorelines.

Out of all the coastal cells studies, three have been chosen: Nouakchott (Mauritania), Aveiro (Portugal) and Delfland (the Netherlands). The Nouakchott cell was split into a north and south side. These cells have in common that they all have a littoral barrier at one of the boundaries of the coastal cell with the assumption that there is no sediment transport. Due to this assumption, the LST could be calculated for each coastal cell. Nouakchott North experienced an annual sediment transport of 0.66 million m3 between 1985 and 2020, a volume increase of 23.01 million m3. Conversely, Nouakchott South experienced an erosion rate of 0.92 million m3 per year, resulting in a total loss of 32.36 million m3 over 35 years. In this same period, the Aveiro shoreline has accumulated a volume of 17.83 million m3 of sediment. In addition, the Aveiro shoreline displayed significant fluctuations compared to Nouakchott.

The Delfland coastal cell is the most complex coastal area among the three selected cases due to two littoral barriers at the boundaries and the anthropogenic measures in the past 37 years. This results in a volume increase of 45.55 million m3, similar to the beach nourishment volume of 46.51 million m3. As a result, it can be concluded that only the beach nourishment is visible in the SDS data, even though shoreface and dune nourishments have also been carried out during this period.

The findings indicate that the SHORECAST model, which incorporates the "Single-line theory" and specific boundary conditions, can generate multiple predictions. This makes it a universal tool for estimating sediment transport over time, even with future anthropogenic measures. It is important to note that not all assumed zero boundaries in sediment transport are zero in reality. Apart from SDS data, other shoreline position data can be integrated into the model to achieve similar results. Further research is needed to explore the possibilities of improving the understanding of different boundary conditions, thereby enhancing the obtained outcomes and the practicality of this study. An important suggestion is to explore the feasibility of identifying littoral barriers and other boundary conditions. This would make the developed model more robust and widely applicable.

In recent decades, a growing number of shoreface nourishments have been carried out along the Dutch coast to mitigate coastal erosion. Designing shoreface nourishments requires a comprehensive understanding of their complex morphological evolution to develop optimal solutions. However, accurately predicting this evolution in Delft3D-FM has proven challenging. Excessive flattening of nourishments in morphological process-based models leads to an inaccurate representation of the cross-shore profile, and the implications of this inaccuracy on longshore predictions remain unclear. To address this issue, a hybrid model has been developed that seamlessly integrates a data-driven component into the process-based numerical model Delft3D-FM through Basic Model Interface. Contrary to previous study efforts, the focus is not on improving the representation of physical processes, but on incorporating a data-driven component into Delft3D-FM to more accurately represent observed behavior in cross-shore modeling. The presented modelling framework facilitates the prevention of excessive flattening of shoreface nourishments in Delft3D-FM by enabling user-defined manipulation of bed level changes during simulation. The hybrid model is then applied to reproduce a shoreface nourishment at the coast of Ter Heijde for two main objectives: (1) to demonstrate the proof-of-concept of a hybrid model approach and (2) to examine how inaccuracies in cross-shore modelling affect longshore predictions, thereby highlighting the added value of a hybrid model approach.
The results demonstrate the proof-of-concept of the hybrid model. Unlike the standard model, which showed excessive flattening of the nourishment, the hybrid model maintained its nourishment shape and followed observed cross-shore evolution over three months of morphological modelling. We found that a hybrid model approach has the potential to more accurately represent the nourishment’s lee effect, which plays a crucial role in the morphological response to a shoreface nourishment. By preventing excessive nourishment flattening, larger waves break earlier and/or more frequently in the hybrid model, causing a calmer wave climate in the lee of the nourishment compared to the standard model. As a result of increased wave sheltering, the flow velocity in the lee reduces which causes sediment supplied supplied by longshore currents to settle at a higher rate compared to the standard model, leading to increased sedimentation in the nourishment’s lee.
As a result of the enhanced representation of the lee effect, the alongshore redistribution of sediment differs between the hybrid model and the standard model. After three months of morphological modeling, differences of 10-25% between the models attributed to the nourishment sediment are observed in the lee of the nourishment. Additionally, the hybrid model shows a trend of increasing divergence from the standard model over time. This indicates a sustained added value of the hybrid model over time.
This thesis represents a contribution towards a data-integrated approach in process-based modelling of the complex evolution of shoreface nourishments, highlighting the potential added value of such an approach. Therefore, we anticipate this thesis to be a starting point for more sophisticated ways to incorporate accurate cross-shore evolution in numerical models in the context of shoreface nourishments.

This thesis explores the potential of a fixed artificial bypass system for a sustainable and eco-friendly approach to coastal management in IJmuiden. The presence of the IJmuiden Port disrupts the natural processes, causing significant morphological changes to the coastal area. Current management practices require frequent dredging and nourishment to mitigate the erosion of the downdrift coast and maintain the depth necessary for navigation in the channel and port. These activities result in significant emissions and adverse ecological impacts. Particularly affecting benthic life, organisms living in or on the seabed.


Implementing a fixed artificial bypass system, already proven successful in similar projects globally, emerges as a potential solution to reduce dredging and nourishment activities. This system aims to restore the natural sediment transport by pumping sediment from the updrift to the downdrift side. In addition, its more continuous discharge of sediment is anticipated to be less disruptive for benthic life compared to traditional nourishment methods.

The best-case scenario calculation performed in this thesis presents that an artificial bypass system at IJmuiden could potentially reduce dredging activity by 3.5% and nourishment activity by 37%. To assess whether these reductions can be achieved, this thesis introduces a newly developed framework for assessing the effectiveness of sediment bypass concepts based on four performance indicators: (1) Dredging Activity of Channel and Port, (2) Sediment Demand of Downdrift Coast, (3) Impact on Benthic Community and (4) Feasibility.



This method includes simulating the response of the coastal system after implementing varying bypass concepts using a Delft3D model. The Delft3D model’s applicability and predictive skill are assessed via hydrodynamic and morphodynamic validation. Concluding that the model can reproduce the general trends but introduces numerical errors in the exact quantification of the morphological development. Despite this limitation, the output from these Delft3D simulations was used to evaluate the response of different artificial bypass concepts based on the four performance indicators. The first two indicators are based on the simulated sediment transport values and assessments of the development of the bed. The evaluation of the third indicator is based on a calculation performed using the developed benthic evaluation tool, named the 'Benthimeter'. This newly developed tool provides a method that intends to visualize and quantify the impact on the benthic community induced by nourishment activity. Although the Benthimeter requires further calibration and validation, it marks a good first step towards integrating ecology into coastal management.


The results of this thesis demonstrate that the coastal system of IJmuiden allows for sediment withdrawal, where allready 10% of the required annual sediment trap was observed within one simulated month. Also northward sediment dispersal towards the downdrift coast was observed at simulations, indicating that such a system could reduce the sediment demand. These findings provide confidence that the principles of bypassing sediment around the port of IJmuiden hold. Consequently, it is anticipated that an artificial bypass system would, to some amount, reduce the need for dredging and nourishment activity. Also, the calculated impact on the benthic community confirms the hypothesis that a more continuous nourishment approach reduces the impact on the benthos. While the findings of this study provide an initial indication of the potential effectiveness of an artificial bypass system at IJmuiden, they do not provide long-term effect estimates. Further research is suggested to examine the primary drivers of dredging and nourishment activity, along with efforts to simulate the equilibrium state to evaluate the long-term effects.


The most important contribution of this thesis is the introduction of innovative tools, guidelines, and effective methods. This framework can be used in future research to improve our knowledge of sustainability and ecology in coastal practices.

Flood defense will have to be strengthened all over the world as sea level rise poses great challenges for the safety of coastal settlements. Strengthening traditional hard flood defenses is becoming increasingly more difficult due to limited space in the coastal zone and large costs inflicted with renovation. Adaptive ‘soft solutions’ pose an alternative as they make use of natural processes that are able to adapt to changing boundary conditions. The Prins Hendrik Sand Dike is a pilot project of such a soft solution placed in front of an existing hard sea dike. The Prins Hendrik Sand Dike is the subject of this research.
This research strives to identify the role of waves, currents, and water levels on morphological development of the Prins Hendrik Sand Dike. Which requires an identification of the morphological development during the 3.5 years of service lifetime. This is followed by a characterization of the forcing climate based on measured on-site data. This knowledge is used to hindcast the full forcing climate during the PHSD lifetime and calculate morphological development. Lastly, a comparison of calculated and observed morphological development reveals suitability of engineering formulae on low-energy beaches.
Results indicate the spit head develops at a faster rate than predicted in model studies. In addition, constant erosion in the form of coastline retreat is observed in a section that serves as primary sea defense. These findings hamper successful development of habitat and possibly decrease the longevity of the sea defense if maintenance is not performed. Furthermore, waves have been determined to be the dominant forcing mechanism resulting in sediment transport and morphological development. In addition, systematic water level changes that occur under specific wave conditions are identified causing increased Northeastward transport of sediment. These findings likely explain discrepancies between the previously modelled and observed morphological development.
Implications of this research contribute to an understanding of the interconnected nature of forcing scenarios at low-energy beaches and can be used to improve modelling efforts of low-energy beaches. Furthermore, it provides a basis for Hoogheemraadschap Noorderkwartier to make decisions on maintenance activities.

Echosounders are used to monitor suspended sediment concentrations (SSC) in coastal management studies and to monitor dredge plumes. Due to the dependency on sediment properties like particle size, shape and density, performance of single frequency measurements is limited when sediment properties are changing.

Using multi-frequency measurements, mean particle sizes can be derived and used to (partly) adapt to these variations. Based on field measurements in the coastal waters around Texel, performance of the single and multi-frequency methods was assessed under steady and varying measurement conditions.

While similarly high performance was obtained under steady conditions, the multi-frequency method outperformed the single frequency method significantly when measurements were taken over multiple tidal stages. Also, SSC estimations became less sensitive to selection of frequency. If further developed, the potential of SSC quantification using echosounders is significantly increased.

The coastal safety of the dunes are of high importance for low laying countries (Chen et al., 2017). This is especially true for the Netherlands as it is used officially as a safety measure against flooding from extreme weather since 1984 (Rijkswaterstaat, 1989). As of current 1D modelling of the waves is an acceptable method for the Dutch coast to assess the safety of the dunes (Den Heijer, 2013). For assessing the dune coastal safety the 98t h percentile of the runup R2% (Stockdon et al., 2006) is used for defining the wave response during a storm on the dunes. The current dune coastal safety studies consider bound waves (infragravity and sea- swell waves) propagating from offshore to nearshore. However, due to the Dutch coast being located at a very large semi-enclosed basin additional free infragravity waves can be present during a storm next to the bound waves that are reflected from other coasts (Daouk, 2020) as leaky waves (Herbers et al., 1995), and potentially increasing the R2% magnitude. Here we show that the R2% with the additional free infragravity waves in the wave domain can have a significant response on the dune coastal safety. The additional free infragravity waves can have tens of centimetres of R2% magnitude increase that is dependent on the slope of the domain. For the additional free infragravity waves a higher R2% is observed for steeper slopes, while a larger R2% growth is observed at the milder slopes when the free infragravity waves are initially introduced to the slope. The dune coastal safety assessments conducted thus far do not consider the effects from leaky waves from other coasts, therefore underestimating the safety provided from the dunes against flooding. With the research conducted by considering additional free infragravity waves with the traditionally bound waves originating in a storm, a better insight can be provided for dune coastal safety. As a result, companies and governmental bodies such as Rijkswaterstaat in the Netherlands that assess the coastal safety of the dunes can benefit by having a more complete representation of the coastal hydrodynamics that can as a result prevent flooding or provide dune nourishment after the episodic event (Sallenger, 2000).

Accurately predicting the surface transport in the ocean is crucial for estimating the course of marine pollution, which is considered one of the most pressing environmental issues of the 21st century. In the ocean, floating marine pollution is transported by several mechanisms, including waves. Current models predicting the surface transport set the wave-induced transport component to be equal to the Stokes drift, which is defined as the net drift that a fluid parcel experiences in the direction of a propagating wave. However, Deike et al. (2017) and Pizzo et al. (2019) indicated that the transport induced by the Stokes drift is enhanced by breaking waves. Despite extensive study of the wave breaking phenomenon, it is still not possible to accurately predict the surface transport for breaking waves in deep water irregular seas. Thus, in this thesis, the contribution of the transport from breaking waves to the total wave-induced transport at the surface of a deep-water unidirectional irregular sea is estimated. To do this. a theoretical model is developed. The model computes the transport of individual breaking wave groups from surface elevation measurements of a deep-water unidirectional irregular sea. Thereafter, the contribution of the wave-induced transport from breaking to the total wave-induced transport is defined by an enhancement factor. This enhancement factor shows how much the total surface transport in a wave field without breaking waves is enhanced by the transport of breaking wave groups.

The model that is developed is an extension of the relationship from research by Sinnis et al. (2021). In their research, they defined a transport relationship for isolated breaking wave groups based on the spectral bandwidth and the linear slope of the wave groups. In the model, the transport relation from Sinnis et al. is applied to the breaking wave groups from surface elevation measurements of deep water irregular seas. In order to do this, the surface elevation spectrum was approximated by multiple Gaussian wave groups. From the Gaussian wave groups, the spectral bandwidth and the linear slope could be determined. The breaking waves were identified based on a steepness threshold for the wave groups. The wave-breaking-induced transport was calculated for all individual breaking wave groups.

Additionally, experiments were carried out to validate the theoretical model. The experiments were performed in the Atlantic Basin of Deltares. In this facility, unidirectional irregular waves were generated in deep water. During the experiments, an overhead camera filmed the behavior of quasi-Lagrangian particles floating on top of the waves. The particles were tracked using OpenCV and their trajectories were obtained. Because the particles in breaking waves travel faster than in non-breaking waves, a velocity threshold was used to identify the breaking waves in the trajectories. From the identified breaking waves the wave-breaking-induced transport was quantified.

Furthermore, the theoretical model was validated by comparing the number of breaking waves, the strength of the breaking events, and the enhancement factor with the experimental results. The results showed that all values were in the same order of magnitude and that the wave-breaking-induced transport enhanced the surface transport for non-breaking waves by a factor up to 1.5. Besides, a sensitivity analysis on the relevant parameters showed that the error margin remains within 10% from the mean. In conclusion, the theoretical model gave reasonable predictions of the contribution of the wave-breaking-induced transport in a unidirectional irregular sea. Hence, this framework can be fruitful grounds for further extension of the breaking induced drift in the ocean.

An increasing amount of the worlds coastal regions suffer from structural erosion due to anthropogenic influences. A prime example for this phenomenon is the Oosterschelde, Netherlands, where the partial closure of an estuary lead to a decline of the local intertidal flats, threatening the valuable functions they provide as an ecosystem and for shore protection. A sustainable measure to slow down the decline, is the usage of wave disrupting oyster reefs, which reduce the wave energy on the flat, thus reducing erosion. As of now, the conditionality and extend of the wave attenuation effect of such reefs is still widely unknown. This is thwarting a more extensive usage of oyster reefs for erosion management, since the actual effects of such a reef are highly uncertain prior to construction. This thesis was designed to investigate and quantify wave attenuation capabilities of an artificial oyster reef in a macrotidal environment, improving the understanding of the impact of such structures on their physical environment. A wave analysis was carried out on a reef using field data, allowing for the quantification of attenuation, the identification of processes, a parameterization of the results and an insight on the predictability of attenuation. Extensive field data was acquired on seven locations on a transect over the investigated reef, including pressure and velocity data. The reef was built using shell filled wire gabions and is orientated perpendicular to the main wind direction. It has dimensions of approximately 120 m length, 8 m width and 0.8 m height. The reef crest is located 0.5 m above mean low water level and 2.3 m below mean high water level, being emerged approximately 30 % of the time. Incoming waves are characterized by maximum significant wave heights of 0.8 m and maximum mean periods of 3 seconds. Wave attenuation was quantified by comparing the energy flux in front of (seaward) and behind (shoreward) the reef under different hydrodynamic conditions. The conditionality of attenuation was found to be best represented by the relative submergence ds /Hm0,i , which represents the ratio of the freeboard on top of the reef and the incoming wave height. Attenuation was found until a ds /Hm0,i ratio of approximately 4. Compared to the bare tidal flat in front of the reef, the reef attenuated energy up to 40 times more effectively per distance. The spatial footprint of the reef was found to vary strongly with different ds /Hm0,i ratios, but being roughly of the same order of magnitude as the reef length. Reflection, overtopping, wave breaking and friction were identified as the main mechanisms behind energy attenuation. An attempt to parameterize these was done using dimensionless numbers, which can be used to predict attenuation by using incoming wave, and reef characteristics. The determined processes were best represented by the parameters ds /Hm0,i and L01 /ds. Three empirical relations describing wave attenuation over breakwaters were used to investigate whether existing formulas can predict wave attenuation over the observed oyster reef. The measured and calculated results show a strong correlation of R ~ 0.9 but need to be tuned to reach reasonable root mean square errors. This implies that such existing formulas can be adjusted to represent oyster reefs, making them a possible tool to predict oyster reef performance in the future. The findings show that the present oyster reef is effective in attenuating waves and contribute to the overall understanding of how oyster reefs can reduce erosion. A better insight on the quantity of attenuation and the spatial footprint of the reef's effects was achieved. The footprint of the reef's effect is hereby limited to an area close to it, meaning that the reefs impact on erosion should not be overestimated. Such a reef should thus rather be seen as a complementary measure against erosion, stabilising the local area. As a next step, setting up a numerical model is recommended, where the wave attenuation can be linked to actual erosion quantities. Quantitative research on additional oyster gabions can further be used to refine existing empirical relations, creating some predictability of transmission values over oyster reefs.

The erosion of the seabed in front of coastal structures induced by waves can lead to multiple types of failure instability or function of the structure. On this topic most research has been done into erosion in front of vertical structures. For sloping structures a knowledge gap exists in the understanding of the processes that lead to erosion of seabed material directly in front of the structure. In this report the structural and hydraulic paramters that influence the development of a scour-deposition pattern in front of sloping structures is tested. For this model tests have been done in the wave flume of the laboratory of Hydraulic Engineering at Delft University of Technology. This has resulted in a design formula that can be used for a first estimation of the maximum scour depth in front of sloping coastal structures where bed-load transport is dominant. Parameters that are used in determining this depth are the number of waves, the incident significant wave height, the relative water depth and the reflection coefficient of the structure. Performance of the formula with the model test results is good.

The Delft real-time GNSS single-frequency precise point positioning (RT-SF-PPP) algorithm is extended to include velocity and receiver clock drift as unknown states to be estimated from Global Navigation Satellite Systems (GNSS) measurements. Carrier-phase ambiguities are assumed constant over time. Two different variance models are used, one obtains variance as a function of satellite elevation, and the other obtains variance as a function of carrier-to-noise density ratio as estimated by the receiver. The elevation based variance model was used in the original RT-SF-PPP algorithm, and adapted to include Doppler measurements. The carrier-to-noise density ratio based variance model components are estimated from double difference (DD) observation combinations using measurements obtained from a shortbaseline experiment with two receivers setup over multiple days. Two velocity observables are used and related to velocity and clock drift through the extended functional model of the original algorithm: the receiver generated Doppler and a time-derivative of the carrier-phase observable: the time-differenced carrier-phase (TDCP). Algorithmic performance is evaluated by the horizontal RMSE, which represents accuracy as the variance plus bias squared, precision and reliability. This was validated using three different experiments: a stationary receiver on top of a roof, a buoy freely adrift in the North Sea, and a receiver mounted on a car driving a regional road. It was found that in terms of position in the static experiment and under calm water conditions during the drifting buoy experiment the horizontal RMSE was between 0.429 and 0.530 [m], and under rough water conditions and a road partly flanked by fences and trees between 0.682 and 0.812 [m]. Furthermore in terms of velocity it was found that the TDCP observable in combination with the carrier-to-noise density based variance model has a horizontal RMSE between 0.014 and 0.068 [m/s] over all experiments, and using the Doppler observable with either variance model a RMSE between 0.033 and 0.122 [m/s]. The algorithm was even found by means of external reliability to be capable of detecting faults at the boundary of 0.5 [m] for position and 0.1 [m/s] for velocity in the TDCP observable case.

For both developed and developing nations, coastal zones form an attractive location for urban settlements. With the expected increase in the earth’s population, coastal areas will experience a further increase of inhabitants. Floating city development could therefore be an interesting alternative for land-based urban expansion on land [41]. Expanding an urban settlement towards the ocean however, will make it more susceptible to extreme forces such as a tsunami waves. By generating more knowledge on how a floating structure interacts with a tsunami wave, it can show the potential value that a floating city can bring. If a floating city limits the effect of (extreme) events such as tsunamis, it can protect the coastal zone which is located near a floating city. To provide an answer to this question, this research will focus on how a floating structure can reduce the transmission of a tsunami. With the construction of an analytical model, representing the floating structure and the tsunami wave as simplistic as possible, the system can be understood more quickly. If the problem is solvable by generic programming language, this would mean that it can solve a larger range in the spectrum of the problem. The conceptual model features two options: one where the platform has no freedom of movement, the other where the platformcan move vertically. They both assume that hydrostatic pressure holds during wave propagation and a linearization of the momentum equation describing the water particle interaction. For each option, the transmitted wave height is determined based on varying the floating structure dimensions. This gives an indication on which parameters are of influence in the transmission of the wave. First, the conceptualmodel is analysed by changing the platformdraft and the length for both the motionless and the vertically moving platform. Both options are influenced most by the length of the structure. The situation with the motionless platformshows this effect earlier, by a higher wave attenuation percentage for the same platform length. Whether the draft also has an influence is strongly dependent on the value representing the length of the platform. The difference between the two platform movement options shows that the effect of changing the allowed movement of the platformis significant. Next to the reduction in transmission, the conceptual model shows signs of resonance. The moving platform option in the model is formed by a second order differential equation. Fitting this equation, resonance is evident and therefore visible for certain combinations of the platformdimensions. In addition damping is present, ensuring that there are some parts where, despite the natural frequency pointing there, no resonance occurs. The amount of damping is strongly linked to the platformlength, with a higher level of damping for a longer platformlength. Finally, the results from the conceptual model are compared to the outcome in SWASH. This numerically based model has the possibility to simulate a tsunami wave in its development towards the coast and also features a buoyancy function for structures. This comparison serves as a validation of the conceptual model. In general, the conceptual model always results in a less reduced wave attenuation percentage and can be said to be more conservative. Due to the assumptions of leaving out the non-hydrostatic pressure and a lower level of detail, a maximum of 5% deviation in both model results occured. This however, matches with the fact that it is a less detailed model and adds to the reasoning that the conceptual model provides what it is meant for. Next to the effect of the structure itself, the positioning of the structure is also of large importance. Wave height and intensity of the wave will vary due to the surrounding local coastal features. Next to that, the local water depth is determinant in compressing the wave, therefore decreasing the wave length when the water depth decreases. The maximum wave attenuation that can be achieved according to both models is 10%, considering platform dimensions and location variations. The conceptual model appears to work for which it is intended: modelling the resulting transmission between a floating structure and a linear tsunami. It is expected that modelling programs can be expanded and/or improved, so that more realistic floating structures can be modelled. However, it will remain difficult to accurately model a tsunami as it is complex in behaviour. Yet, this research brought the field one step closer to evaluating the transmission of tsunami waves when interacting with a floating structure of certain dimensions.

About 80-90% of U.S. East Coast barrier beaches have experienced erosion in the last 100 years. South Carolina’s coastline forms no exception, a third of its developed shoreline experiences erosion. Among these eroding shorelines is Hilton Head Island, the second largest barrier island on the U.S. East Coast. Until now, erosion here has been addressed through traditional local beach nourishments. An alternative approach to the traditional nourishment method, are so-called feeder nourishments or feeder beaches. The potential advantages of the feeder nourishment concept over the traditional method are reduction of the nourishment frequency, containment of the ecological stress in a relatively small area, and a short to medium term increase of local available space for recreation and the environment. Given the potential advantages above, the residents of Hilton Head Island asked TU Delft to investigate the possibility of applying a feeder nourishment at their shoreline. Currently, a pilot project known as “The Sand Engine” is examined along the Dutch coast. Several studies into its morphological behaviour show that this feeder nourishment can be beneficial to the sediment budget of a larger coastal cell. Because of the promising results at the Sand Engine pilot project, it is tempting to state that a feeder-nourishment could also be applied at Hilton Head Island. The problem, however, is that the conditions at Hilton Head Island and the Sand Engine are different. There are two main differences between Hilton Head Island and the Sand Engine. First, Hilton Head is subjected to a relative calm wave climate in comparison to the Sand Engine. Second, the presence of two tidal inlets at Hilton Head, compared to a relative straight and uninterrupted coastline at the Sand Engine. As a result, the conclusions drawn from the Sand Engine pilot project do not necessarily hold for Hilton Head Island as well. The main objective of this thesis is to analyse the morphological behaviour of a feeder nourishment located at Hilton Head Island. First, to study its potential as a measure against erosion at Hilton Head. Second, to compare its morphological behaviour to that of the Sand Engine. And third, to be able to examine the potential of the concept for the Atlantic southeast coast of the U.S. in general. The morphological development of a feeder nourishment at Hilton Head Island was simulated with Delft3D over the course of 1 year for different model scenarios, with varying forcing conditions and varying bathymetric features. The effect of the relative calm wave climate at Hilton Head Island in comparison to the Sand Engine is twofold. First, the contribution of wave forcing to the total erosional volume of the feeder nourishment after 1 year is smaller as compared to the Sand Engine. Eliminating all driving forces besides wave forcing reduces the total erosional volume to 58% at Hilton Head, in comparison to 75% at the Sand Engine. Second, the contribution of storm events to the total erosional volume after 1 year from the feeder nourishment is smaller at Hilton Head compared to the Sand Engine. It measures 23% at Hilton Head, in comparison to 60% at the Sand Engine. To assess the impact of the two tidal inlets on the feeder nourishment, they were closed off. Closing of the tidal inlets eliminates any (potential) residual currents. This reduces the total amount of sediment that is eroded from the feeder nourishment by 7% compared to a reference scenario with open tidal inlets. Before construction of the feeder nourishment the coastline south of the nourishment experienced a net sediment outflux of approximately 4000 m3/year. After construction of the feeder nourishment, the southern section experiences a net import of sediment of approximately 100.000 m3/year. Meaning that the southern section, on average, has transitioned from being erosive to accreting. Up to 500 meter away from the nourishment the cross-shore profile shows a seaward movement of the shoreline position of approximately 25 m compared to the original situation without nourishment. Before construction of the feeder nourishment the coastline north of the nourishment experienced a net sediment outflux of approximately 40.000 m3/year. After construction of the feeder nourishment, this net outflux of sediment has decreased to approximately 25.000 m3/year. This shows that the feeder nourishment is feeding sediment to the northern section, but at a rate that is not sufficient to keep up with the underlying erosion rate. The northern domain, on average, still experiences a sediment outflux and stays erosive. Roughly 50 m of coastline directly north of the feeder nourishment experiences a seaward movement of the shoreline position. However, moving further away from the nourishment, the shoreline remains erosive. The Atlantic southeast coast of the United States is made up of North Carolina, South Carolina, Georgia and Florida’s east coast. The South Carolina and Georgia coastline are comparable in both hydrodynamic conditions and geomorphological setting. They are mixed-energy coasts, broken up by numerous tidal inlets, and home to short barrier islands with complex sediment transport patterns. North Carolina’s and Florida’s east coast are wave-dominated, with relative straight shorelines. Which is distinctly differences from the conditions found at Hilton Head Island. Therefore, the potential of the feeder nourishment concept is only analysed for South Carolina’s and Georgia’s coastline. The presence of numerous tidal inlets leads to strongly varying conditions along the coastlines of both states. The developed locations along South Carolina’s coastline that require erosion mitigating measures are south Debidue beach, North Island, Hunting Island and Daufuskie Island. Along Georgia’s coastline there are only some erosion hotspots along Sea Island’s coastline that require erosion mitigation measures. The wave climate at all the above mentioned location is similar to Hilton Head. A southeast swell, with a narrow range of directions and an annual wave height of roughly 1,0 m. The same goes for the tidal range. The results at Hilton Head show that erosion on adjacent coastal sections can be lessened and/or prevented by constructing a feeder nourishment. Given that these locations are subjected to similar conditions, the construction of a feeder nourishment could potentially be an effective measure to prevent or lessen the occurring erosion.

Plastic pollution in aquatic ecosystems is a global problem. Rivers transport large quantities of litter from land to the oceans. Plastics of different sizes and properties are widely present at various locations in river systems. Concerning macroplastics, previous studies mainly focussed on floating plastics, however, substantial parts of the litter can be transported underneath the water surface. Currently, this suspended litter load remains understudied. Submerged litter is presently monitored with the use of nets. The use of nets has several disadvantages. In large rivers, nets can usually, not be deployed over the full depth and width of the river. Moreover, using nets is labour intensive and requires fixed structures to be deployed. To overcome this problem, this thesis aimed to develop and test a new method for monitoring submerged riverine litter. In accordance with the fish detection abilities of sonar, it seems to have a high potential for identifying suspended underwater objects.

In this study, the litter detection ability of a low-cost single beam echosounder (Deeper CHIRP+) were investigated. Three different experiments were executed, in specific, controlled tests in an artificial environment, semi-controlled tests in a natural environment and litter monitoring in a naturally flowing river. The controlled tests, to get an insight into the scanning technique and detection abilities of the echosounder, were performed in the Kerkpolderbad in Delft. During these tests, the influence of actual object size, object depth and flow velocity on the sonar signal was investigated. The semi-controlled tests were carried out in the Rio de San Pedro, in Andalusia, Southern Spain. During these tests, several plastic targets were used and repeatedly released in the river, passing the sensor. For this, objects of different material properties and sizes were used. Lastly, plastic was monitored in the Guadalquivir and Guadalete rivers in Andalusia. In the Guadalquivir river, the sensor was operated together with nets for validation purposes. In the Guadalete river, monitoring took place for 18 hours from a pedestrian bridge, at different locations over the cross-section of the river and under varying tidal conditions.

The performed tests showed a significant relationship between the dimensions of the reflection signal, derived from the sonar observations and the actual object size. However, object orientation and deformation play a role and lead to deviations in the signal dimension results. A second relation, regarding flow velocity and signal dimensions, was observed. The larger the flow velocity, the smaller the sonar signal. Additionally, signal intensities can, for four out of the eight objects tested, be related to material properties but differences in signal intensities are relatively small. Regarding the river monitoring activities, suspended litter items can be counted, river tide is influencing litter transport and litter is present over the full river depth.

The following main conclusions are drawn based on this research:
- Echo sounding can be used for detecting suspended riverine macroplastics. Litter items can be counted, and fish can be discarded from the sonar readings by their specific displayed shapes.
- Litter size can be estimated when looking at the sonar readings, however, several factors, such as flow velocity, object orientation and deformation have to be taken into account when estimating litter size.
- In the Guadalete river, significantly more suspended litter is transported when river water flows into the sea compared to river water flowing inland. The counted litter items were approximately uniformly distributed over the river depth.

In general, using echo sounding for suspended litter monitoring is potentially useful to gain a better understanding of the suspended litter transport, from which prevention and mitigation strategies could be optimised. For further research, it is recommended to use an echosounder for which the raw sonar data can be exported as a standard digital file. Moreover, the set of test objects should be extended, including more variation in object size. To separate signal size and signal intensity, objects of different size but same material properties and objects of the same size but different material properties should be used for testing. Finally, other types of sonar such as side scan or multibeam sonars may potentially lead to more accurate sonar readings regarding litter size and material estimations.

This report presents the results of a research concerning long waves in the North Sea. ‘Long waves’ in this research is a collective name for various types of waves that are longer than the well-known sea-swell waves, here referred to as ‘short waves’. Wave types that are referred to as long waves are infragravity waves, meteo-tsunami’s, seiches and tides. Besides their extensive length, they distinguish themselves from regular sea-swell waves by the mechanisms responsible for their generation and the scale of their impact. Whereas short waves are generated by wind, long waves are generated by short wave-group forcing, the breaking of short waves nearshore and large atmospheric pressure variations. Long waves play a crucial role in the processes of coastline erosion and the breaching of flood defenses, as well as in the formation of rip currents and seiches. These events can lead to severe damage to hydraulic structures and possibly even casualties. A better understanding of them is thus vital for coastal safety.
Rijkswaterstaat has been collecting data regarding the occurrence of long waves on the North Sea for over a decade. Their measurement campaign started in a time when digital broadcasting signals and digital storage space were not well developed yet, making sending and storing the water surface elevation time-series not feasible. The data is therefore filtered by a FIR filter, reducing the size of the data, but also reducing the information that is contained in the data. All frequencies of approximately 0,0125 퐻푧 and higher are removed by the FIR filter. As a consequence a significant part of the infragravity signal is missing and it is not possible to perform a bispectral analysis (used to determine the bound long wave contribution). Nowadays, digital broadcasting signals and digital storage space have plenty of capacity to send and store the data, making the filter unnecessary.
Analysis of the spatial- and temporal distribution of long waves in the North Sea, shows that the majority of long waves have a yearly averaged significant wave height of 2,4 - 3,3 cm and a yearly averaged mean wave period of 125 to 140 cm. Based on data from the full decade, a clear trend in the spatial distribution of long waves cannot be distinguished, offshore and nearshore locations show approximately the same long wave properties. The seasonal analysis shows that the mean significant long wave height averaged out over all locations per season varies from 2,8 cm during summer, 2,9 cm during spring, 3,3 cm during winter to 3,5 cm during fall. For the mean wave period, the mean value averaged out over all locations per season varies from 127,5 s during summer, 128,1 s during spring, 135,6 s during winter to 136,3 s during fall. Predictions of the extreme wave conditions show that the significant wave height with a return period of 10.000 years (Dutch design condition for coastal flood defenses) are around 40-60 cm, although there is quite some uncertainty in these predictions. This uncertainty is due to a relatively short measurement period, usually 30 years of data is used for extreme wave predictions, and remarkable observations in the data.
Time-series analysis of the hourly significant wave height of long waves and predicted bound long waves (Hasselmann, 1962) (Hasselmann, 1963) shows that during mild weather conditions significant wave heights of long waves are low, with minimal contributions by the bound long waves. At the onset of a storm, the significant wave height of both long waves and bound long waves rapidly increase. At the end of the storm, they decrease to the pre-storm values. This shows that the generation of long waves occurs mainly during heavy weather conditions. Hourly significant wave heights of long waves, and especially bound long waves, show a strong correlation with significant short wave heights. The relative contribution of bound long waves (퐸푏푙푤/퐸푙푤) during a storm increases up to values of 60%, which is considerably higher than contributions of bound long waves found in other studies (Herbers et al., 1994). The high ratio of the relative bound long wave contribution, in combination with very low bound long wave activity during mild conditions, shows that the generation mechanism involving wave-group forcing is a major generation mechanism of long waves in the North Sea.

In the Waal bed degradation occurs, which is mainly induced by a large number of river regulations measures done in the past. Rijkswaterstaat develops possible measures and new techniques to stop riverbed erosion and/or mitigate the negative effects. One of the possible new techniques to reduce riverbed erosion locally is groyne field nourishments. The objective for this research is to deepen insights how groyne field nourishments provide enough sediment to the river such that bed degradation locally does not develop further. The following research question is formulated for this: How can groyne field nourishments act as small feeder nourishment that release sediment slowly to the main channel? To answer the research question a literature study is done and a XBeach model is set-up. The literature study is done to obtain knowledge about the hydrodynamic and morphodynamic processes in a groyne field in case of emerged and submerged groynes. From this literature study it appears that the effect of navigation on the morphology in a groyne field is dominant over the effect of the river discharge when the groynes are emerged: net sediment is transported from the groyne field to the main channel mainly by suction. When the flow conditions increase and the groyne get submerged, the effect of navigation on the morphology in the groyne field decreases rapidly and the net sediment transport is from the main channel to the groyne field induced by the river discharge, mainly the large-scale eddies. Extra literature study is done to possible relevant coastal and river processes to get knowledge of the effects of waves and currents on the behaviour of nourishments in a groyne field since very limited research has been done before on groyne field nourishments. It appears that especially dune erosion and river bank erosion by waves and currents can be used to explain how nourishments erode by the primary and secondary ship wave system. After the literature study a XBeach model is set-up of for a series of emerged groynes on a straight section in the Waal. The model is calibrated and validated with data from Rijkswaterstaat and literature. In this model three possible nourishments with the same volume are applied at different locations in the groyne field: 1) one upstream in the groyne field; 2) One downstream in the groyne field; 3) And one in the middle of the groyne field. From this research it can be concluded that groyne field nourishment at all three locations can work as small feeder nourishment that release sediment slowly to the main channel in the case of emerged groynes for about 200 days per year. The nourishment placed in the centre of the groyne field appears to be the most effective nourishment, since 1) the waves and currents induced by navigation attack the nourishment along all its edges, 2) the centre nourishment causes in almost the whole groyne field an increase of sediment transport to the main channel and 3) the flow pattern in the groyne field is changed favourably for the sediment transport of already suspended sediment to the main channel. This research should be seen as first indication if nourishment could work at all. It is advised to research the material of the nourishment and to simulate the groyne field nourishments for a longer period, such that more flow conditions and more ship passage are included, to get a more complete picture of how groyne field nourishments act as small feeder nourishments. Furthermore a practical test with a centre nourishment is recommended to collected data of the hydro- and morphodynamics in a groyne field with nourishment.

This report presents the methodology and findings of a study on the impacts of free long waves on dune erosion predictions in XBeach. In this paper a distinction is made between two types of infragravity waves: bound infragravity waves and free infragravity waves. Bound infragravity waves are generated by short-wave group forcings and are bound to the propagation of the wave groups. Conversely, free waves are infragravity waves that are released from the wave-group in the surfzone, reflect at the shoreline, and propagate back out of the surf zone. In a semi-enclosed basin with mild bathymetric changes such as the North Sea, free long waves that reflect off one coast can propagate large distances and impact other coastlines.

Modelling the response of a coastline during a storm event requires an offshore boundary condition that represents the incident short and long waves. The boundary condition for the incident infragravity waves is often derived by assuming a local equilibrium between the directionally spread sea-swell waves and bound infragravity waves following the K. Hasselmann (1962) method. This approach has proven to be problematic for two main reasons. First, the method tends to overestimate the incident infragravity wave height by assuming a local equilibrium is achieved at the model boundary; however, observations have shown that the transfer of energy from the short-wave groups to the underlying bound wave is gradual on a sloping bed. Second, by applying the equilibrium K. Hasselmann (1962) method it is implied that only bound infragravity waves are present at the boundary underestimating the total incident infragravity wave energy.

An analysis of XBeach in surfbeat mode revealed that the model can confidently predict infragravity wave behaviour on a natural beach slope with two well-developed bars during a storm event by calibrating the roller breaker slope coefficient and wave breaker coefficient. Infragravity wave heights were reasonably accurately predicted in the surfzone, but the model generally overpredicted the most energetic infragravity waves.

Further, the study investigated the impact of free infragravity waves on dune erosion predictions by simulating the behaviour of two 1D planar beach slopes to the inclusion of free long waves at the boundary. The study revealed that on a beach with a 1:35 slope the relative increase in dune erosion volume was 44.1% when the bound infragravity energy is equal to the free infragravity energy relative to the case excluding free waves. For the same conditions, a 20.6% increase was observed in the maximum runup. For a milder 1:70 slope a 36.4% and 6.1% increase in dune erosion and maximum runup was observed.

The results demonstrate that the dune response of a coastline is sensitive to the inclusion of incident free infragravity waves at the boundary. Moreover, neglecting the presence of free infragravity waves at the boundary may underpredict the dune response during a storm event.

On the seabed in front of coastal structures sediment movement takes place due to incoming waves. The erosion of sediments creates a scour hole at the toe of structures such as embankments, breakwaters and dikes. This scour hole may lead to instabilities in the main structure due to material sliding into this hole. A common method of protecting against scour is the placement of a rubble mound toe structure and bed protection. The goal of this study is to better understand the background and main parameters that leads to scour, to predict the (location of the) maximum scour depth and how this is influenced by the bed protection. Consequently, the main research question of this thesis is: What is the expected, wave induced, scour depth over time in front of a sloped embankment, and what is the effect of a scour protection on the (location of the) maximum scour depth?

All over the world coastal communities are at risk due to sea-level rise and intensifying weather conditions. Many sandy beaches are eroding as a result of human-induced factors. Currently, the preferred coastal protection measure in the United States are beach nourishments. In Europe, there also is a general shift from hard to soft coastal protection measures. However, beach nourishments are not a long-term solution. Recently, in the Netherlands, a new concept called a large-scale (mega-feeder) nourishment has been introduced (the Sand Engine). Numerous studies on this new concept have been conducted. However, not for a mega-feeder nourishment nearby a tidal inlet system. About 10\% of the world's beaches consist of barrier islands. Emphasizing the importance of investigating the development of a mega-feeder nourishment nearby a tidal inlet system, under various hydrodynamic conditions. Therefore the research question is as follows: “How does a nearby tidal inlet system influence the development of a mega-feeder nourishment?” The research question is answered by investigating the effects various hydrodynamic conditions have on the development of a mega-feeder nourishment nearby a tidal inlet system. This is done for fixed morphodynamic features, such as the dimensions of the tidal basin and the dimensions and orientation of the tidal inlet. The only variable morphodynamic feature is the alongshore position of the mega-feeder nourishment. Four distinct hydrodynamic scenarios are modelled to investigate their effects on a mega-feeder nourishment. The tidal range (η), significant wave height (Hs), peak wave period(Tp) and peak wave direction (Dp) are varied. This resulted in the following hydrodynamic scenarios: 
•Mild wave conditions: (η = 1.5m; Hs=1.0m and Dp=0°);
•Oblique wave conditions: (η = 1.5m; Hs=1.0m and Dp=-45°);
•Storm wave conditions: (η = 1.5m; Hs=variable and Dp=0°);
•High tidal range: (η = 3.0m; Hs=1.0m and Dp=0°).
These hydrodynamic conditions and their effect on a mega-feeder nourishment are modelled by utilizing a process-based numerical model called Delft3D. In Delft3D, two locations of the mega-feeder nourishment per hydrodynamic scenario are evaluated. A mega-feeder nourishment is placed at an alongshore distance of 2 kilometers and 5 kilometers from the tidal inlet. This to get insight in the tidal flow nearby a tidal inlet and up to what alongshore distance this tidal flow affects the development of a mega-feeder nourishment. The hydrodynamic conditions were simplified, meaning steady wave characteristics and a single M2 tidal constituent. Using real time-varying hydrodynamic conditions yields similar results compared to the simplified hydrodynamic conditions. Therefore, simplifying the hydrodynamic conditions is justified. The results show that there will be additional erosion near a tidal inlet if the mega-feeder nourishment is located inside the influence of the tidal inlet. The influence is the alongshore distance where the currents owing to the tidal inlet (residual currents) still affects the total alongshore sediment transport (larger than 50 m³/6y/m). The alongshore distance of the influence increases with an increasing tidal range (tidal prism). However, there is no shoreline retreat owing to the tidal inlet at the location (2km from the tidal inlet) of the mega-feeder nourishment over a time period of 6 years. Only the adjacent coast on the inlet-side of the mega-feeder nourishment erodes significantly more than without a tidal inlet, with an increasing magnitude in the shoreline retreat towards the tidal inlet. Hence, it is expected that if the mega-feeder nourishment is placed close to the tidal inlet (i.e. several hundreds of meters), then the influence of the currents owing to the tidal inlet will enhance the shoreline retreat at the location of a mega-feeder nourishment. To conclude, the tidal inlet does influence the development of a mega-feeder nourishment nearby a tidal inlet (order several hundreds of meters). However, this is not necessarily seen in the retreat of the shoreline but instead in deeper depth contours. The governing process in the sediment transport at a mega-feeder nourishment is the incident wave angle for small tidal ranges (η < 1.5m) and mild wave conditions (Hs > 1m). However, for a large tidal range (η > 3.0m) the residual currents owing to the tidal inlet will become the governing process.